Theodore H. Eaton, The Ancestry of Modern Amphibia…
“ Naef (1929) considered the rib-bearer a derivative of the basiventral, which, by spreading laterally and dorsally to meet the neural arch, enclosed the vertebral artery. He then supposed that by reduction of the rib-bearer in other tetrapods (frogs and amniotes) the vertebrarterial foramen and costal foramen were brought together in a single foramen transversarium. The implication is that the Urodele condition is primitive, but it cannot now be supposed that Urodela are ancestral to any other group, and the rib-bearer is most probably a specialization limited to salamanders. ”
